1. Field of the Invention
The present invention relates to solenoid operated hydraulic valves and in particular to techniques for damping the operation of such valves.
2. Description of the Related Art
Solenoid operated valves have been developed for a variety of equipment to selectively apply and exhaust pressurized fluid to and from a component, the operation of which is controlled by that valve. One type of such valve has a spool that slides within a bore. In one position, the spool provides a path between a supply conduit containing pressurized fluid to a workport that is connected to the component being operated by the valve. In another position, the spool provides a path between the workport and an exhaust port to relieve pressure at the workport. In a third position of the spool, the workport is disconnected from both the supply and the exhaust ports.
In many applications relatively high pressure acts on the spool and other components of the valve which can produce large forces that adversely affect the operation of the valve and the longevity of those components. As a consequence, these valves often include a damping mechanism to restrict the rate at which the spool and solenoid components operate, thereby reducing the adverse affects that high pressure forces have on the valve components. Such damping devices also provide stability to the valve operation under a range of pressure levels.
In a typical valve, the armature moves within a central bore of the solenoid. In order for that motion to occur, fluid in a chamber on one side of the armature must flow to a chamber on the opposite side of the armature in order to provide space for the armature motion. In the most simplistic form of damping, a fixed orifice is provided between the chambers, thereby restricting the rate of flow and thus the velocity of the armature. However, satisfactory damping control with a fixed orifice is often difficult to achieve for systems, such as in outdoor equipment, in which the viscosity of the fluid varies with respect to temperature. In other words, the fluid at relatively high temperatures has a low viscosity and thus can flow more freely through the fixed orifice, as compared to when the fluid has a lower temperature and a higher viscosity.
Therefore, it is desirable to provide a damping mechanism that yields a more uniform damping over a wide range of operating temperatures and fluid viscosities.